1. Field of the Invention
The present invention relates to a sheet conveying device and an image forming apparatus, and more particularly, a sheet conveying device suitable for a document conveying device for conveying a document sheet to a scanning position of an image reading device at a conveying speed at which the image can be read, and relates to an image forming apparatus using the sheet conveying device.
2. Description of the Related Art
In the past, a sheet conveying device serving as a document conveying device capable of separating each sheet from a bundle of cut sheet-like document sheets, and continuously feeding the sheet to an image scanning position of an image forming apparatus such as a copier, a facsimile machine, and the like, is well known. In this kind of sheet conveying device, a known sheet conveying device is one having a paper feeding belt and a separation roller used in a mechanism for separating a document sheet from the document bundle and pressing a holding in which a paper feeding belt is set in a direct manner or with a link mechanism so as to change a separation pressure which is set by a contact angle (nip angle) of a nip portion between the paper feeding belt and the separation roller.
For example, Japanese Patent No. 4152604 discloses a mechanism for releasing pressure of a paper feeding belt while preventing skew and adjusting a contact angle at a nip portion of a separation roller using a pair of cams provided in a proximity of the paper feeding belt so as to allow adjustment of the contact angle of the nip portion between a paper feeding belt and the separation roller using this pressure release mechanism.
However, in such sheet feeding device and image forming apparatus capable of feeding sheets continuously as described above, the separation pressure which is set by the contact angle of the nip portion of the paper feeding belt and the separation roller of the separation feeding device can be changed and set, but the contact angle at the nip portion of the paper feeding belt and the separation roller thus set cannot be accurately maintained while the sheets are being passed. For this reason, the contact angle of the nip portion of the paper feeding belt and the separation roller may change while the sheets are fed, and there is a problem in that the separation pressure may change.
Accordingly, the present invention is to provide a sheet conveying device and an image forming apparatus capable of appropriately holding a contact angle of a nip portion of the paper feeding belt and the separation roller during separation of sheets and obtaining preferable separation pressure at all times.